Reports on Maker of Artificial Heart Shake Up Its Stock

PARIS — The stocks of biotech and medical device start-up companies are notoriously volatile. And the French company Carmat, which has been trying for years to bring an artificial heart to the market, felt that pull on Friday as investors bid up its stock.

The shares of the company, Carmat, were initially suspended when buy orders swamped the market after French news media reports, citing unidentified sources, said that surgeons had implanted one of the devices in a second human patient. The company’s spokeswoman, Caroline Carmagnol, declined to comment.

Initially rising as much as 19 percent, the stock — after trading resumed — ended the day at 89.69 euros, or about $120, a gain of 10.66 percent for the day.

Wild rides are not uncommon for shares of Carmat, which was founded in 2008, has been publicly traded since 2010 and has never made money.

There was a similar one-day spike in stock in July, when the company announced it had received permission from the French authorities for a resumption of human trials. That word came after the death in March of a Carmat heart recipient who lived for 74 days after doctors in Paris implanted the device.

Carmat has been developing a “bioprosthetic” heart made of synthetic materials and animal tissue, under the guidance of Alain F. Carpentier, an internationally known expert on heart valve replacements. The company received early backing from the Airbus Group, the French government’s innovation fund and Truffle Capital, a venture firm.

Carmat’s device is meant to treat patients with terminal heart failure, a common and frequently fatal condition in which the organ is not strong enough to pump blood efficiently throughout the body, leaving patients weak and short of breath.

The French newspaper Libération and the radio station France Inter reported on Thursday that the company’s second implantation procedure had been carried out in great secrecy three weeks ago by Daniel Duveau, a thoracic surgeon at the University of Nantes, and that the procedure had gone well.

Vimla Mayoura, a spokeswoman for the thoracic unit at the university, referred inquiries to the company.

After the death of the first Carmat patient, Dr. Carpentier hypothesized in a newspaper interview in March that a short circuit had caused the man’s death. Carmat said it had been studying the data gleaned from that operation before it went back to the authorities for permission to continue with the human trials.

So far, human heart transplantation is the only treatment for chronic terminal heart failure, which affects an estimated 20 million people in the United States and Europe. But the supply of suitable donor organs meets only a small fraction of the need.

The Carmat device, called a “total artificial heart,” is operated by electric motors. Sensors inside the body are used to adjust its pumping action to that like a normal heart, while a device replaces the two lower chambers, or ventricles, of the organ.

The first such device, the Jarvik-7, was implanted in a human patient in the early 1980s. An Arizona company, SynCardia, has continued its development. A Massachusetts company, Abiomed, makes another device, the AbioCor.

To date, such devices have been used mainly for “bridging” — the time between removal of a patient’s diseased heart and when they actually undergo a transplant. Carmat’s differs in that it is meant to be capable of doing away with the transplant altogether.

But Robert Littlefield, a medical devices analyst at GlobalData, said there continued to be major challenges to creating successful artificial hearts, which he described as “immensely complicated devices with many possible places” for things to go wrong.

SynCardia has a few advantages, he said, including the creation of a pediatric version, while Carmat’s device could prove to be too large to fit the chest cavities of many women and most children.

Ultimately, “this is a last-resort device,” Mr. Littlefield said. “It’s for people who are on their last legs, so the market isn’t very deep.”